The present invention relates to a new and improved construction of a twin pusher centrifuge.
In its more specific aspects, the present invention relates to a new and improved twin pusher centrifuge comprising a sieve or filter drum which is rotatable about its lengthwise axis at a predetermined rotational speed and which contains a product infeed and product discharge outlets at both its ends. Approximately at the center of the sieve or filter drum there is arranged a pusher or thrust floor member which rotates about the sieve or filter drum axis at a rotational speed which is different from the rotational speed of the sieve or filter drum. The marginal zone of the pusher or thrust floor member which faces the inner wall of the sieve or filter drum is designed to form a line which extends at least once to-and-fro between extreme positions in the direction of the lengthwise axis of the sieve or filter drum and serves to push or displace the product along the inner wall of the sieve or filter drum.
In pusher centrifuges as known, for example, from U.S. Pat. No. 2,232,770, granted Feb. 25, 1941 or U.S. Pat. No. 4,073,731, granted Feb. 14, 1978, a planar pusher or thrust floor member is arranged normally relative to the lengthwise axis of the sieve or filter drum and is periodically reciprocated or moved to-and-fro in axial direction. The product is supplied through a product infeed located close to the pusher or thrust floor member and is periodically pushed or displaced in the direction towards the product discharge by means of the oscillating to-and-fro reciprocation movement of the pusher or thrust floor member. The centrifuge thus can be continuously operated. However, a complicated and expensive mechanical or hydraulic drive system is required for periodically reciprocating the pusher or floor thrust member, and considerable energy is consumed for moving the masses. The mass forces occurring in conjunction therewith cause an unsteady operation of the centrifuge and the exertion of high loads upon the bearings. Furthermore, the movement of the pusher or thrust floor member in only one direction is used for discharging the product.
In another construction of pusher centrifuge as known, for example, from U.S. Pat. No. 2,350,041, granted May 30, 1944, the aforementioned disadvantages can be partially eliminated by replacing the reciprocating pusher or thrust floor member with a pusher floor member which is arranged at an inclination with respect to the sieve or filter drum axis and which rotates at a different rotational speed. In this case the pusher or thrust floor member performs a wobbling or wobble movement relative to the sieve or filter drum. Due to this wobble movement the product is further displaced or transported at the individual locations at the sieve or filter drum in a similar manner as in a pusher centrifuge containing a reciprocating pusher or thrust floor member. Since the transport of the product occurs in a timewise-shifted manner around the circumference of the sieve or filter drum and since there are only provided rotational movements without continuous acceleration and deceleration of masses, such a centrifuge containing an inclined pusher or thrust floor member has a lower energy consumption and a more steady or quieter operation.
In modifications of the last-mentioned pusher centrifuge as described, for example, in German Pat. No. 1,065,333, granted Sept. 10, 1959, the pusher or thrust floor member is designed, for instance, with a corrugated or undulated marginal zone such as to extend to-and-fro more than once in axial direction. The displacement or stroke frequency is thus multiplied in comparison to a single floor member arranged at an inclination which has a displacement or stroke frequency corresponding to the difference in rotational speeds. Furthermore, there is described a twin pusher centrifuge in which the pusher floor member is arranged at the center of a sieve or filter drum provided with discharge openings at both its ends. This pusher or thrust floor member either is arranged at an inclination or is provided with a marginal zone extending to-and-fro. By using such a design there is utilized the movement of the pusher or thrust floor member in both directions. Thus, the output of the centrifuge is nearly doubled and a relatively steady or quiet run is obtained due to the symmetrical structure. However, it is a disadvantage of this construction that a product infeed has to be provided on each of the two sides of the pusher or thrust floor member which is arranged at the center of the sieve or filter drum. The product infeed into the centrifuge thus occurs simultaneously on two opposite sides, however, using separate product infeeds which makes the construction complicated and expensive. Furthermore it cannot be ensured that the product infeed on the two sides always remains exactly the same, which causes disturbing asymmetries and requires the use of an expensive automatic control for the product infeed.